Thanks Chaadster, very detailed response!

I'm guessing the 53 would be the better fit for me.

my current bike: 543 ETT , 73 HT, 73.7 ST
53 lemond: 545 ETT, 73 HT, 73 ST

Seems like it's close enough that I should be able to make it fit with saddle fore/aft and stem height and length adjustments better than going with the 55.

I think people have gotten used to smaller frames these days to so theory on fit is different. When I look at old forum posts from when these bikes were current people with pretty similar measurements to me where going with 55 and even 57 Lemonds. A lot of personal preference I guess.